Anthony Santoro

Urbanisation has a wide range of impacts on biological communities, which can affect individual animals' health and may lead to population declines if health effects cause decreases in lifespan or reproductive output. Here, health metrics of the southwestern snake‐necked turtle ( Chelodina oblonga ), a freshwater turtle endemic to and declining in southwestern Western Australia, were compared among populations from three wetlands in the Perth metropolitan area that differ in degree of urbanisation. In November 2023, 7–10 adult turtles were trapped in each of the three wetlands, scaled body condition was calculated, and a blood sample was collected from each individual to quantify blood glucose concentration and immune function, measured as bactericidal capacity, and baseline physiological stress level, measured as heterophil: lymphocyte ratio. There was no association between degree of urbanisation and any of the health metrics measured, suggesting that adult C. oblonga in populations from more natural habitats do not exhibit higher body condition, greater immune functioning or lower baseline physiological stress levels than adults from more disturbed habitats, and that impacts on individuals' health are likely not directly driving the apparent lack of recruitment observed in urban populations of this species. However, El Niño‐induced drought conditions during the sampling period may have placed additional environmental stress on all populations, not just those in more urbanised areas, potentially masking differences in health that may have been detectable in years more reflective of mean climatic conditions. An important next step is to quantify potential seasonal and interannual changes in health metrics across a wider range of populations and hydrological regimes to determine the magnitude to which drought conditions impact physiology in this species, the extent to which physiological plasticity may buffer individuals against negative health impacts, and whether physiological plasticity differs along a broader gradient of anthropogenic disturbance.

Context
Obtaining a source of genetic data is a key constraint in population genomic research.

Aims
In this study, single-nucleotide polymorphisms (SNPs) were generated from oblong turtle (Chelodina oblonga) cadavers, to ascertain whether decomposed tissue could be used as a source of genetic data and to investigate genetic variation.

Methods
Tissue was opportunistically collected from 47 cadavers following a mass mortality event during April 2024 at Bibra Lake, Western Australia. Genotyping was performed using a Chelodina DArTseq platform, with a high-density assay of 2.5 million sequence reads.

Key results
Genetic diversity and inbreeding were investigated for 39 individual C. oblonga, using 8053 SNPs retained from data filtering. Observed and expected heterozygosities (HO = 0.26, HE = 0.31) for C. oblonga were relatively low compared with other freshwater turtle species within Australia. A high inbreeding coefficient (FIS = 0.17) was also detected, suggesting that inbreeding may threaten C. oblonga population viability at Bibra Lake.

Conclusions
This study highlights the utility of decomposed turtle cadavers as a viable source of DNA.

Implications
Management plans should implement strategies to improve gene flow between Bibra Lake and adjacent populations, such as establishing wildlife corridors to encourage migration between populations.

Turtles are declining globally, and absences of juveniles during surveys are often interpreted as evidence of threats to early life stages. In Australia, for example, it is widely argued that a low number of juveniles is likely due to nest predation by introduced red foxes (Vulpes vulpes). However, small sample sizes within populations, low detectability of juveniles and turtles' long lifespans often confound the conclusion that a paucity of juveniles indicates a declining population. Because turtles have long reproductive lifespans, we might intuitively expect most turtle populations to be heavily weighted towards large individuals, but a ‘typical’ or ‘healthy’ size distribution for turtle populations has not been well established.

Therefore, we collated data on 41,021 freshwater turtles from 38 species and 428 populations located in parts of Australia both with and without introduced foxes, as well as populations in the United States of America, which naturally have raccoons (Procyon lotor), foxes and other nest predators. We examined population-level body size distributions to establish a baseline for ‘typical’ turtle populations and test whether populations that are exposed to introduced foxes have proportionately fewer juveniles compared to both AU populations that lack introduced foxes and USA populations that are naturally exposed to nest predators.

We found that most turtle populations in AU and the United States were heavily skewed towards adults and had few juveniles, regardless of the presence of foxes or other nest predators. There were, however, clear differences among population survey methods: those that target shallow areas (e.g. crawfish traps) tended to capture proportionately more juveniles, and small sample sizes (∼<50) often produced inaccurate representations of size distributions. Additionally, we used a simulation to demonstrate that, given common turtle life history parameters, even stable populations should generally have low proportions of juveniles.

Based on our results, we encourage caution when interpreting turtle size distributions. A small number of juveniles does not inherently suggest that a population is declining due to high egg and/or juvenile mortality, and researchers should pay careful attention to the biases in their methods and strive to capture a minimum of 50–100 turtles before drawing inferences.

Freshwater turtles are one of the most threatened vertebrate groups and face multiple threats including habitat loss, predation, and road mortality. Wildlife Detection Dogs (WDDs) have been used to aid in conservation globally. However, their use for freshwater turtle conservation has received minimal research attention. This descriptive study explores the efficacy of using a WDD to locate both turtles and nests, to protect them from mortal threats. A WDD was trained to detect turtle-related odours, specifically female turtles, eggs, and nests. Deployment at two wetland sites in Western Australia resulted in the successful location of 10 live turtles and 26 nests, with the WDD actively searching for 36.17 hours. Limitations during the odour learning and training phase, such as the absence of crucial nest odours and challenges during mass-nesting days, may have limited the number of nests detected. Other challenges that need to be considered include ground disturbance, contamination, and safety in snake habitats. Recommendations include obtaining soil plugs and lowering target odour thresholds for training, minimizing odour learning on live turtle odours, and optimizing deployment strategies to improve WDD efficiency with a focus on nest detection. The study provided insights into the potential use of WDDs in turtle detection and underscores the potential of WDDs as a tool in enhancing conservation efforts for freshwater turtles.

Freshwater turtles are crucial to aquatic ecosystems and among the most threatened vertebrates globally. As wetlands are increasingly affected by urbanisation and climate change, translocating turtles may become increasingly common to prevent population declines. Freshwater turtle responses to translocation remain poorly understood. This study examined the movement responses of the southwestern snake‐necked turtle, Chelodina oblonga , following relocation from a wetland slated for urban development. We radio‐tracked 40 of 268 turtles translocated to two wetlands, monitoring them for up to 228 days and analysing movement responses in relation to size, sex and release wetland using generalised linear models. Over half (54%) of the tracked turtles permanently left their release wetlands, and 38% homed back to their original wetland via a 3.2–7.0‐km estuarine river and a steep, ~15‐m high terrestrial bank. Movement out of the release wetlands was unrelated to turtle size or sex but significantly influenced by release wetland. Homing probability was not affected by size, sex or release wetland. Turtles were more likely to leave the release wetland closer to the source, possibly due to its smaller size or drying conditions. Release wetland significantly influenced the timing of both 'any' and 'homing' movements. Sex affected the timing of both movement types, while size influenced only 'any' movement timing. The study highlights that the characteristics of translocation sites are important in retaining translocated turtles. The study adds to the limited understanding of the movement responses of translocated freshwater turtles and has direct implications for the design of translocation programs.

Human activities and climate change are altering wetland hydrology, potentially affecting freshwater turtle habitats. Understanding freshwater turtle habitat requirements is important for conservation. Chelodina oblonga, a freshwater turtle endemic to southwestern Australia, inhabits wetlands undergoing hydrological changes due to reductions in rainfall and urbanisation. Urban populations of C. oblonga are declining, but limited knowledge of their habitat requirements hinders conservation efforts. This study used radio-telemetry to determine the habitat associations of 100 adult female C. oblonga in three urban wetlands with varying hydrological regimes between 2018 and 2020. During wetland inundation, turtles occupied dense stands of two emergent macrophytes: Typha orientalis (naturalised, invasive) and Machaerina articulata (native). When wetlands dried, turtles aestivated in shallow areas beneath these plants, contrasting with previous reports that aestivation occurred within the deepest areas. As inundation was the trigger for emergence from aestivation, some individuals in the shallowest areas aestivated for > 581 consecutive days and missed a reproductive season. This study indicates that complex vegetation is key aquatic and aestivation habitat for female C. oblonga, and alterations to hydro-regimes, particular increased drying, may have severe implications for isolated freshwater turtle populations through limiting recruitment. Hydrological regimes that incorporate an annual wetted period are recommended for conserving C. oblonga, in view of projected ongoing drying of wetlands due to climate change. Maintenance and restoration of dense emergent macrophyte stands, preferably the native M. articulata, is recommended to help conserve C. oblonga populations in wetlands that regularly retain surface water in the future.

Freshwater turtles are one of the most endangered vertebrate groups with >60% of species threatened globally. Terrestrial nesting habitat degradation is a major threat to freshwater turtles, but the characteristics of nesting habitat remain poorly understood. This study investigated the nest site selection of the southwestern snake-necked turtle (Chelodina oblonga) to improve the conservation prospects for this species in an urbanized wetland area.

In total, 235 depredated and 86 non-depredated nest sites and 320 non-nest locations were surveyed at Bibra Lake, Western Australia, during the Austral spring–summer, 2018–2023. A suite of environmental variables was measured at nest sites and non-nest locations. Analysis of similarities was used to determine whether nest sites and non-nest locations differed in their environmental characteristics. Generalized linear mixed models were used to identify environmental variables that best explained the nesting preferences.

The environmental characteristics of nest sites differed from those of non-nest locations, with turtles nesting mainly in remnant natural habitat with greater canopy cover. Turtles generally avoided nesting in modified environments such as lawns and impervious surfaces.

Factors influencing nest site selection are probably associated with the conditions necessary for regulating incubation temperatures and ease of nest excavation.

This study suggests that modification of terrestrial vegetation around wetlands is adversely affecting freshwater turtle recruitment by removing or altering preferred nesting habitat. Protection and restoration of natural habitats fringing urban wetlands is important for the conservation of remnant freshwater turtle populations, and local partnership projects can help to achieve this.

Australian freshwater turtle populations have declined substantially, with consequent losses to aquatic ecosystem functions. A leading hypothesis is that turtles have declined through lost recruitment caused by high nest predation by invasive foxes. The ‘fox hypothesis’ is supported by experiments showing that nest predation rates exceed 95% in many regions. Furthermore, population surveys have repeatedly found absences of juvenile turtles, and headstarting experiments have successfully replaced those juveniles in some species. We are currently leading a nationwide citizen science program, ‘1 Million Turtles’ (1millionturtles.com), to engage local communities to protect turtles from threats like nest predation using a suite of novel approaches. Our key innovation is to leverage community passion and interest for turtles to create positive conservation impacts via a nationwide support network. We provide a data collection tool and framework (TurtleSAT) and self-guided training in conservation methods. We assist with guidance for gaining licencing and permission, and applying for grants. We are evaluating our approach through both the impacts on turtle populations as well as through surveys of our engaged citizen scientists. Ultimately, we aim to create a science-supported, national grassroots conservation model where community champions can lead their own evidence-based approaches to help wildlife.

Roads affect the connectivity of habitat and inhibit movements of animals as a result of road avoidance and road-related mortalities. Freshwater turtles are particularly vulnerable to mortality on roads, as females must often cross them when they leave the aquatic environment to nest. Ecopassages designed to enable safe movement across roads by wild animals may be an effective measure to reduce adverse impacts. Limited information exists, however, on effective design criteria for freshwater turtles.

A willingness-to-utilize study was used to assess factors that may influence the use of a tunnel underpass by the southwestern snake-necked turtle (Chelodina oblonga), a species whose populations are declining, in part, through road-related mortalities of nesting females. Female C. oblonga were sourced from an urban wetland and placed in an enclosure with exits of varying tunnel lengths (12 and 25 m) and lighting treatments (‘light’ and ‘dark’) to assess the conditions that would promote successful passage.

Generalized linear modelling showed that light treatments had a significantly increased likelihood of successful and faster passage for both 12 and 25 m tunnels than the dark treatments. Tunnel length had no effect either on success or rate of passage.

This study provides the first account of the factors that may optimize successful tunnel passage by C. oblonga to reduce road-related mortality, contributing to the conservation and management of the species and freshwater turtles more generally.